connection: fix getpid() call on disconnect

[mkmkme]

Previous fix only handled the connections from Valkey class, which left classes like Sentinel broken because those are handled in AbstractConnection.
Also after merging previous fix I was pointed to the place in Python standard library where the similar issue was handled by having from os import getpid instead of having a local object assigned to os.getpid.

Fixes #158

Pull Request check-list

• Do tests and lints pass with this change?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?

Description of change

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 76.22%. Comparing base (ef40c56) to head (a2c27a9).

Files with missing lines	Patch %	Lines
valkey/connection.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
- Coverage   76.23%   76.22%   -0.01%     
==========================================
  Files         130      130              
  Lines       33947    33946       -1     
==========================================
- Hits        25879    25877       -2     
- Misses       8068     8069       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.